Cocaine abuse is a problem of significant concern today. Not only is cocaine one of the most reinforcing substances known, but its chronic use induces the phenomenon of sensitization, a reverse tolerance that persists for months following drug withdrawal. Reinforcement and sensitization contribute significantly to cocaine's addictive properties, and probably underlie the tremendous recidivism of cocaine addicts. Considerable behavioral, electrophysiological, and biochemical evidence indicates that the ventral tegmental area (VTA) and nucleus accumbens (NAc), of the mesolimbic dopamine system, are principal loci mediating cocaine's actions. Knowledge of the molecular changes that underlie reinforcement and sensitization, induced by chronic cocaine within these brain loci, is limited. A wide range of monoamines and peptides, including dopamine, serotonin, glutamate, neurotensin, cholecystokinin, and substance P, are implicated in the actions of chronic cocaine. As well, cocaine has prominent effects on intracellular second messenger systems that are likely to trigger the regulation of a wide range of proteins. The inability to explain the action of chronic cocaine based on currently known systems, and the indication that many as yet unsuspected protein systems are probably affected by cocaine, supports the need to use an inclusive screening methodology, that functions independently of a priori hypotheses, to detect both novel and known cocaine-regulated proteins (CRPs). This proposal develops and utilizes the procedure of subtraction hybridization to enrich for and isolate CRPs in the rat NAc and VTA. CRPs will undergo nucleic acid sequence analysis to determine if they are known or novel proteins, as has been done for several isolated CRPs thusfar. The proteins will be characterized temporally, to determine if CRP regulation occurs with a time course consistent with cocaine sensitization or withdrawal, or whether persistent protein changes can be identified that might underlie prolonged recidivism. A select number of CRPs then will be targeted for further characterization. Anatomical studies will ask whether CRP regulation is specific for the mesolimbic dopamine system or other known neuroanatomical tracts, and will provide an indication of the function of novel CRPs. Pharmacological studies will determine if CRP regulation is specific to chronic cocaine, or drugs of abuse in general, and will be used to define specific neurochemical mechanisms of CRP regulation. CRP regulation will also be compared in rats that receive cocaine by forced-administration and self-administration. CRPs that display altered levels in both paradigms are most likely to represent critical regulatory targets of cocaine. Ultimately, the inclusive characterization of CRPs in critical brain reward regions will provide for a better understanding of cocaine's actions, and should allow for the more logical and efficacious design of treatments for drug addition in general.